In the research of semiconductor, coatings, memories, and displays, the precursor plays an important role to obtain high quality thin films. It controls many parameters and eventually it will affect properties of thin films. The precursors require high purity, high thermal stability, high volatility, appropriate reactivity and low toxicity. Additionally, in processes of thin films, the precursors should vaporize in a limited time and at a reproducible rate for Chemical Vapor Deposition (CVD) or Atomic Layer Deposition (ALD).
In semiconductor areas, Group 5 transition metal-containing films have long been thought for variety of applications. The resistance switching characteristics of MxOy thin films show its potential applications for the next generation nonvolatile resistive random access memory (ReRAM) devices as well as for high-k capacitor applications such as a thin layer in-between ZrO2 layers to reduce leak current and stabilize the phase.
Typical Group 5 transition metal halides have been explored for the deposition of MxOy (M=Nb, Ta x=1-2; y=1-5) by CVD (Thin Solid Film 1999, 343-344,111) or ALD (J. Vac. Sci. Technol. B 2003, 21, 2231, CVD 2009, 15, 269). Those precursors sometimes require high temperature and may not be appropriate as precursors due to etching effects.
Nb(OEt)5 precursor has shown promising results to deposit amorphous Nb2O5 by ALD with a stable temperature windows of 230-260° C.) (CVD 1998, 4, 29). In addition, the precursor has been used to study mechanism NbxOy ALD depositions using H2O or D2O (Langmuir 2010, 26, 848). In case of Ta(OEt)5, ALD of Ta2O5 with H2O has shown a process window between 170° C. and 230° C., having amorphous phase at 600° C., as deposited and crystalline phase at 800° C. (Microelec. Eng. 2010, 87, 373).
Imido-type precursors are probably most well known and widely used to deposit Group 5 transition metal containing films. Mostly, they are in a liquid phase with high vapor pressure, which is big advantage in industry for vaporizing and transferring to a reaction chamber. Many derivates have been studied for CVD (CVD 2008, 14, 334, CVD 2000, 6, 223, ECS Tans. 2008, 16, 243) or ALD (Chem. Mater. 2012, 24, 975).